Very little is known about the neurophysiological mechanisms that regulate behavior and homeostasis for long periods of time (hours and days). OUr ignorance of these fundamental and medically important processes is due, in part, to the lack of experimental preparations in which cellular-level studies can be performed over appropriately long periods of time. From a mollusk, Aplysia californica, we have developed a model system for analysis of these mechanisms in vitro. In the abdominal ganglion of this animal a discrete group of peptidergic neurons, the "bag" cells, strongly infoluence the activities of other central neurons. These neuronal effects last for hours, they are of multiple types (excitatory and inhibitory), and they are mediated, in part, by peptides released from th bag cells on stimulation. One clearly advantageous feature of this model system is that the targets of the bag cell system are identified neurons in neural circuits that are already well defined. Thse circuits regulate several visceral and somatic organ systems, including the heart, respiratory organs and ink gland. Since bag cells are known to trigger a complex and long-lasting behavior (egg-laying), a behavioral role for this peptidergic neuroendocrine system is already strongly implicated. The immediate aim of our research is to describe the effect of stimulated neuroendocrine activity - the bag cell after discharge - on motor outputs and behaviors related to egg-laying. We will study this interaction in semi-intact preparations where each of the three components in the response system - peptidergic cells, their target neurons, and the regulated organ systems - can be observed and manipulated experimentally. These studies will provide detailed information concerning the cellular mechanisms of a long-lasting and complex behavior. Our ultimate goal is to understand the functions of individual neuropeptide messengers in regulating these behaviors.